Avoid O(n^2) behavior in cidr_merge when many ranges can be merged
Avoid O(n^2) behavior in cidr_merge when many ranges can be merged

Deleting items at the beginning of a list has O(n^2) behavior.
When deleting begins at the end of the list, we have O(n) instead.

mlecours/netaddr,braaen/netaddr,bluetib/netaddr